Eukaryotic and prokaryotic cell structure

What it shows

All cells have a plasma membrane, cytoplasm, ribosomes and DNA, but they organise them differently. Prokaryotic cells such as bacteria have no nucleus: their DNA lies in a nucleoid with no membrane around it, often alongside small plasmids, and their ribosomes are the smaller 70S type. Eukaryotic cells enclose their DNA in a nuclear envelope and contain membrane-bound organelles such as mitochondria, endoplasmic reticulum and the Golgi apparatus. Plant cells also have a cellulose cell wall, chloroplasts and a large central vacuole, while animal cells lack a cell wall but have centrosomes and lysosomes. In Measure mode the drawing is treated as a micrograph printed at a stated magnification (plant cell ×1,000, animal cell ×2,500, bacterium ×25,000), so magnification = image size ÷ actual size; the scale bar shows the same scale. Assumed sizes are typical: plant cell 50 µm, animal cell 20 µm, bacterium 2 µm. The Close-ups tab shows structures too small for a light microscope as a transmission electron microscope shows them. Cilia and eukaryotic flagella have nine doublets round a central pair of microtubules (9 + 2), moved by dynein arms, and grow from a basal body built like a centriole (nine triplets, 9 × 3). Peroxisomes break down H₂O₂ with catalase; glyoxysomes turn the fat of germinating seeds into sugar. The nucleolus makes ribosome subunits, which leave through nuclear pores. Microtubules (25 nm), intermediate filaments (10 nm) and microfilaments (7 nm) make up the cytoskeleton.

How to use

Choose Plant, Animal or Bacterium and click organelles in the diagram to read their structure and function; the comparison table highlights the same component for all three cell types. Turn Labels off and ask students to name organelles before checking. A useful sequence is to find the parts shared by all three cells, then those found only in plants, then what the bacterium lacks. Then press Measure, drag the ruler across the whole cell and then the nucleus, work out each actual size before reading it, and press Record to build a table for all three cell types. Then open Close-ups (EM), choose a structure and a view, and tap parts to read their roles; turn on Ruler, measure a structure and press Record to fill a table in nanometres. In Cilium → Lengthwise, drag the red section line from the shaft to the basal body and watch 9 + 2 become 9 × 3.

Parameters you can change

• Cell type Plant cell, Animal cell, Bacterium (prokaryote)
• Show organelle labels
• Show comparison table of the three cell types
• Preselected organelle (none), Nucleus, Mitochondria, Chloroplast, Central vacuole, Ribosome, Nucleoid
• Measure mode (ruler, scale bar, magnification)
• Tab Whole cell, Close-ups (electron micrographs)
• Close-up shown Cilium: cross-section (9 + 2), Cilium: lengthwise section, Centriole: cross-section (9 × 3), Centrosome (pair of centrioles), Peroxisome, Glyoxysome, Nucleus: nucleolus and pores, Nuclear pore, Cytoskeleton in a cell, The three cytoskeleton filaments

Questions to explore

1. Which cell structures are found in all three cell types shown?
2. Why is the region containing a bacterium's DNA called a nucleoid rather than a nucleus?
3. What do chloroplasts and a large central vacuole tell you about the way plants live?